BELGRADE, Yugoslavia (CNN) -- As Serbs celebrated the third
most holy day in the Eastern Orthodox calendar, NATO bombing
in Yugoslavia intensified on Sunday, reportedly killing
numerous civilians when missiles hit a bridge in central Serbia.

Local authorities said 12 people died in the attack near the
town of Krusevac. Tanjug, the official Yugoslav news agency,
reported that 11 were killed and 40 injured when three NATO
missiles hit the bridge, which was crowded with vehicles and
pedestrians.

NATO officials confirmed that alliance warplanes struck a
bridge crossing the Velika Morava River near Krisevac on
Sunday. They described the structure as a "legitimate
military target."

A Serbian Web site reported that at least one civilian in the
Serbian town of Vranje was killed in a NATO attack and another civilian was seriously wounded.

Belgrade was reportedly heavily hit again, with air activity
over New Belgrade, Rakovica, Lipovicka Forest, Ostruznica and
Makis.

Serb television showed smoke coming from an area believed to
be Bubanj Potok, east of Belgrade. Four missiles reportedly
hit a television transmitter near Dimitrovgrad in the
Yugoslav republic of Montenegro.

Despite the attacks, Orthodox Christians in Serbia celebrated
Dukhovi, honoring the dead by lighting candles and placing
gifts at graves. Some hung wreaths on their doors, hoping to
ward off bombs.

Amid increasing reports of civilian casualties, NATO's top military commander, Gen. Wesley Clark, said the alliance was
operating under tight rules of engagement, targeting military
sites and not civilians.

"We know which villages are occupied. We know which are not,
and we're going exclusively after military targets. We would never do it any other way," Clark said on CNN's "Late Edition."

Alliance air power again hammered away at Yugoslavia Saturday
night into Sunday morning, flying 697 sorties and scoring 309
strikes during the 68th day of attacks, according to NATO.

NATO military spokesman Maj. Gen. Walter Jertz said continued
good weather helped maintain the increased number and
effectiveness of the mission.

"We have severed their primary lines of communication, so
Serb forces are having to use temporary bridges and other
work-arounds," he said at a NATO briefing.

Jertz said there were indications that Yugoslav military
units were on the move.

"We have reports of relocation and replacement of artillery
units, in particular the 203rd battalion operating northwest
of Nis, an indication that NATO air force has struck those
forces successfully in the past," he said.

NATO spokesman Jamie Shea denied a published report in London
that the alliance would consider introducing ground troops
into the campaign if it had not succeeded by mid-June.

"I think we are talking about the success of the air
campaign, not the defeat of the air campaign," he said.

Shea welcomed Yugoslav President Slobodan Milosevic's
reported acceptance in principle of conditions to end the
bombing set forth by the G-8 nations, the seven leading industrial countries and Russia. But NATO remained wary.

"Details are very important here," Shea said. "Anything that
means that Belgrade moves towards those five (NATO)
conditions is something that we will welcome, but at the same
time we will remain cautious, because details in this
business are everything."

Finnish President Marrti Ahtisaari, who serves as the
European Union envoy to Yugoslavia and accompanied Russian
envoy Viktor Chernomyrdin to Belgrade last week, said a
Kosovo peacekeeping operation would be similar to another in
the Balkans.

"We are talking about an operation that resembles the one in
Bosnia-Herzegovina," Ahtisaari said on "Late Edition."

Shea reiterated that any peacekeeping force introduced in
Kosovo must be controlled by NATO -- a provision not outlined
in the G-8 proposal that Milosevic reportedly agreed to in
principle.

"The refugees will not move unless they see a very strong
NATO presence in that force," he said. "We know fully well
that only a very strong NATO force will be able to provide
the security that's necessary for the reconstruction of
Kosovo."

Clark said any move toward peace by Milosevic was prompted by
the airstrikes.

"This winning of the air campaign is what's propelling the
more or less frantic diplomatic efforts that President
Milosevic is attempting to engage in now in an effort to get
a bombing pause. So it's clear which way this campaign is
going," he said.

Clark dismissed suggestions NATO should halt the bombing,
which some NATO critics contend has stymied diplomatic
efforts, in particular those by Russia.

"It will give them a chance to reconstitute and refit their
forces. It will raise the risk to our NATO pilots when we
resume operations over Kosovo," Clark said.

A top Yugoslav official said NATO has other reasons for not stopping the bombing.

"The insistence of the continuance of the bombing is crystal
clear, that they are opposed to a peaceful resolution of the
problem," said Vladislav Jovanovic, Yugoslavia's charge
d'affaires to the United Nations.

"They are still decided to win one unwinnable and
unauthorized war." Jovanovic said on "Late Edition."

"This is very bad because it is an ominous sign that peace
efforts ... have very powerful enemies in NATO and in some
circuits of the U.S. government," he said.

Meanwhile, NATO plans to again boost its air forces
in the Balkans. The deployment of 68 more aircraft beginning
next week will bring to 769 the number of U.S. aircraft
operating in the Balkans, Pentagon officials said. NATO
forces will have 1,089 aircraft when the deployment is
completed.

Britain plans to redeploy Tornado fighter-bombers from
Germany to the French island of Corsica to shorten the flying
distance to Yugoslavia.